Skimming stones is no idle pastime – Its hard science. Thats the lesson French physicist Lyderic Bocquet passed on to his eight-year-old son. The Lyon University professor came up with a formula that calculates the speed, spin and shape necessary for an optimal skim of a stone. You probably know that flat rocks work best and the faster the stone is travelling, the more times it will bounce. But did you ever consider that spinning creates a gyroscopic effect that prevents the stone from wobbling? Bocquet determined that to bounce at least once, the stone has to be going at least one kilometer per hour. To match the world record, set in Texas in 1992 by Jerdone Coleman-McGhee, who skipped a stone 38 times, one would need a flat stone 10cm in diameter, travelling at a speed of 40 kilometres per hour, spinning at 14 revolutions a second. Impressive!